With the increasing popularity of fuel injection in both diesel and carbureted engines and with the increased emphasis on gas mileage and emission controls, the need to derive accurate information concerning the performance of each engine cylinder has rapidly increased. However, until recent years, great difficulty has been encountered in attempts to obtain accurate information concerning the internal performance of the cylinder during the combustion process. Numerous transducers have recently been devised by the applicant and others for developing the necessary signals from the engine cylinder to be used for diagnostic purposes. For example, U.S. Pat. No. 4,036,050 of applicant Joseph Dooley and Edward Yelke discloses transducers which operate in conjunction with the hold-down apparatus for injector nozzles of the type utilizing clamps or dogs to hold the nozzle in seating engagement with the engine block or head or in conjunction with a screw-in type injector nozzle of the type which is threaded into the engine housing or otherwise secured to the housing by screw-type fittings which are coaxial with the nozzle itself. In some engines, however, the nozzle apparatus is not readily accessible or is of such a shape and size as to make it difficult to adapt existing transducer structures to it. The applicants have discovered that pressure variations from within the cylinder can be alternately detected through the aperture normally provided for glow plugs in many diesel engines or for spark plugs in carbureted engines. Diesel glow plugs are threaded through the engine walls into the combustion or pre-combustion chamber to provide heat from an electrical filament to warm the chamber and thereby enhance the ignition and combustion within the cylinder during cold starting.
For diesel engines utilizing such glow plugs, the applicants have developed a transducer assembly which screws into the engine block in the receptacle normally provided for the engine glow plug. This glow plug replacement transducer is disclosed in the copending application Ser. No. 960,600 filed on Nov. 14, 1978 and entitled Combustion Monitoring System For Fuel Injected Engines. This transducer has also proven quite effective in developing a signal proportional to pressure variations occurring within the engine cylinder during the combustion process. However, the glow plug must still be removed for replacement by the transducer. The present invention eliminates the need for removal of the glow plug while still making possible the detection of pressure variations within the cylinder that are reflected through the passage normally provided for the glow plug. As such, the present invention provides for dynamic timing of the engine at all times and temperatures and under any conditions existing in the field or the laboratory. More important, the transducer assembly of the present invention may, if desired, be permanently attached to the engine to continuously provide information from the engine cylinder to on-board monitoring or control apparatus.
Other transducers for developing pressure-related information from the cylinder through specially modified plugs have been disclosed in the 1978 SAE Journal No. 0098-2571/8605-0054. These transducers have not found wide applicability in that they generally require modifications to existing engine components and are suited primarily for the laboratory.
It is a general object of the present invention to overcome the drawbacks and deficiencies of the prior transducers and diagnostic systems through the provision of a transducer assembly which is specially adapted for use with glow plugs of the screw-in or threaded type. More specifically, it is an object of the invention to provide such a specially adapted transducer assembly in a form that can be utilized without interfering with the normal operation of the associated glow plug.
It is a related object of the invention to provide a transducer and diagnostic system which can be utilized dynamically to develop information concerning the activity within the cylinder during normal operation of the engine, at all times and temperatures and under any conditions existing in the field or laboratory.
It is still a further object of the present invention to provide a diagnostic system which is economical to build and easy to use both in the laboratory and in the field.
It is still a further object of the invention to provide a transducer assembly and associated circuitry which is adaptable to a wide variety of different engines and which can be installed in a permanent or semi-permanent fashion for continuous use within the vehicle.